The Nigerian coast stretches for a distance of approximately 800 km from the tip of
Badagry Lagoon to the eastern end off Cross River near Calabar. It can safely be divided
into a number of distinctive but not separate ecological zones which succeed each other
from the apex ‘A’ to the base ‘B’, as shown in Figure 1:

The Freshwater Zone: rivers, shallow lakes and swamps

The Brackish-Water Zone: creeks, lagoons, rivers and mangrove swamps

The Coastal Zone: beach ridges and estuaries

The Off-Shore Zone: the coastal waters of the sea

A brief description of the physical, chemical and biological characteristics related
to fish culture of each ecological zone as divided above, is to be given below.

The major freshwater rivers of the Nigerian coast include Forcados - Upper Nun River,
Peninnington - Osiaina River, Nun River, Ogbia River, Orashi River and Ogosi River
(Scott, 1966). This freshwater zone is characterised by numerous meandering rivers and
creeks, flowing between levees, behind which lie extensive swamps. This zone is subject to
annual flooding in September–November, during which time most of the area is under water.

The shallow lakes and swamps in this zone are mainly seen in the Delta areas - essentially
a flood plain with meandering rivers which resulted in the formation of ox-bow
lakes and finally to the irregular lake. The lakes and swamps are generally more productive
than the rivers, as it is in the swamps that the more fertile water-borne deposits are laid
down, in contrast to the heavier particles of sand which form the infertile bed-load of the
rivers. Furthermore, the lakes are fertilized by decomposed organic matter derived from
the swamps vegetation which supports an excellent food chain for fishes. This factor
explains why all lakes have a low transparency due to suspended silt. Temperature ranges
from 24° to 31°C, and pH from 6.5 to 8.5. The swamp waters are acidic (pH 4.5–8.5), with
little oxygen content (0.4–2 ppm), but the freshwater rivers have oxygen ranging from 5 ppm to
9 ppm (Scott, 1966) due to water mixing by wind action and increased photosynthetic activity
by water plants. Scott (1966) also stated that the lakes and the swamps in the Delta areas
are poor in minerals. The phosphate content is less than 1 part per million and the nitrate
content is low. Both phytoplankton and zooplankton are very poorly developed as a result of
poor mineral deposits.

Freshwater fish farming in this zone will have some practical problems and constraints.
There are three major requirements to be considered: provision of water to the ponds,
provision of drainage (a minimum mean tidal amplitude of about 0.5 m is available) and
permeability of the soil, since this zone lacks a high clay content in the soil.

The whole of this zone covers the intertidal areas where saline surface water is
encountered. It includes creeks, lagoons, and rivers. The waters of the creeks in Nigeria
are reported to be rich in plankton and organic matter. Besides supporting stocks of
fishes, oysters are common, attached to the roots of the mangrove trees at intertidal levels.
The Nigerian coastline, especially the Delta areas, is extensive but shallow with numerous
sandbanks, some of which are exposed at low tide and are joined to each other by intracoastal
creeks. During the high-flood season, very strong currents sweep down the rivers,
particularly the Nun, Sengana, Ramos and Forcados rivers. The salinity of the estuaries
varies during the year, being considerably higher in the dry season, when sea water
penetrates further up the rivers, than in the wet season, when rain water and the flood water
form the Niger and Benue rivers, and drive the salt water back toward the sea. At the
entrance of some of the rivers, salinity in the dry season is about 26 ppt, while in the
flood season it drops to 2 ppt.

In the south-western part of Nigeria, the intricate lagoon system of water-ways is
included in this zone. It stretches from the Dahomey border to the Niger Delta. During
the rains, an immense volume of fresh water from the Ogun, Oni, Oshun and Saga rivers discharges
into the lagoon system. Hence the salinity ranges from 0.5 ppt to 28 ppt, pH
from 5.5 to 8.5, oxygen concentration from 0.4 ppm to 11 ppm and temperature from 24° to 34°C.
The vegetation around this complex lagoon system in Nigeria is characterized by stilt-rooted
trees with a dense undergrowth of shrubs and by raffia palms (Raphia sudanica) and
oil palms (Elaeis guineensis). The dominant plant species in the swampy areas of the lagoon
include Rhizophora racemosa and Avicennia nitida.

It has been observed that the intertidal region in the creeks and lagoons is very
narrow and the wide expanse of shallow water in the lagoons never drains to expose sand or
mud flats. Because the lagoon system is very shallow, there is little vertical circulation
in the water.

This zone of the Nigerian coast had tremendous potential for fish farming. From
Pillay (1965), Scott (1966) and hydrological data gathered by NEDECO, it is estimated that
the saline swamps in the Niger Delta alone cover 5 048 km2. Pillay's estimate of 500 kg/ha/year would give a total potential yield for the whole unused area of 311 000 ha of about
155 000 t of fish per year. The cost, however, of bringing the whole of this acreage under
management as fish ponds is astronomical. At about US$ 1 235/ha, it would cost about
US$ 384 million. But considering the rapid increase in population and the high demand for
fish in the next few decades, the Nigerian Federal Government could well decide to develop
the more accessible parts of this zone for increased fish production.

This zone is made up of beach-ridges and estuaries. The estuaries in the eastern part
of the Nigerian coast are very extensive and support permanent fishing communities. Some of
the estuaries located at Forcados areas and Bonny-New Calabar areas are fully exploited,
while others are under-exploited, such as the areas located in the Sombreiro, Nun and
St. Bartholomew rivers. Conditions in some of the estuaries of the coastal zone are more
conducive to development than in the creeks. Scott (1966) observed that fishing is better
in the estuaries: there are more people and more permanent settlements, living conditions
are pleasant, fresh water is available, crops may be grown and there is a steady coming and
going of traders in the larger estuaries. In addition to the possibility of increasing the
landings by improving the fishing gears, particularly in set-nets and possibly longlines
for the capture of the large fish, such as croaker and threadfin, the estuaries of this
zone appear suitable for the introduction of trawling from small motor-vessels to exploit
the stocks of fish and small prawns. There is enough room for manoeuvring, the waters are
fairly sheltered and the greatest danger (the sand banks) can be avoided by using an echo-sounder
to fish along given contours.

Fish farming in this zone will have some major constraints because of the choppy
conditions and heavy rainfall which occur in the estuaries.

This zone consists largely of the coastal waters of the sea. In the eastern part of
the country, this zone is 'mainly made up of the Delta platform and the pro-delta slope. The
former extends from the beach to 8–12 km off-shore, a ‘gently inclined, terrace-like feature’.
In general, fine sand and course silt occur inshore and coarser silt and dark grey, clayey
silt further out. This is broken by the rivers and their bars. It is gradually followed by
the pro-delta slope, lying from 8 km to 32 km offshore. This is a fairly smooth sloping bottom
of grey silt inshore gradually changing to finer grey or greenish-grey silt further out.
Beyond these lies the open continental shelf, a generally smooth slope of greyish-green,
silty clays shelving down (Scott, 1966).

The off-shore zone in the western part of the Nigerian coast is immediately followed
by the continental shelf. It is relatively shallow especially in the lower latitudes and
has a gentle slope of about 1.7 m/km. Its width varies from place to place along the whole
stretch of the Nigerian coast. This zone is subject to heavy surf, as it is open to the
full expanse of the Atlantic Ocean, and even in the calm weather of the dry season there is
a persistent swell.

The movements of the fish in and out of the four zones are presumably determined by
changes in salinity, temperature and seasonal breeding migrations. The surface feeding fish
(pelagic) of which the most important are the bonga, ‘sawa’ and shad, move from the sea into
the estuaries as the salinity there rises in the dry season. The larger estuarine fish which
favour reduced salinity (e.g., croaker, snapper, barracuda), appear to move from the
estuaries into the middle reaches of the rivers and into the small creeks in the upper part
of the brackish-water zone at this time. As a result, large-mesh gillnetting in the estuaries
in the dry season suffers, whereas cast-netting and small-mesh gillnets do well. During
the next season, as the rivers rise, the reverse takes place. Large stocks of crustaceans
occur along the Nigerian coast, especially in the eastern part of the country. They live
on the muddy sediments laid down where the flow of the river is impeded by the sea and it
deposits its burden of silt and mud. Prawn and shrimp fisheries have tremendous potentials
in the Niger Delta and in the adjacent coast, the Calabar area to the coast of the Delta,
the Forcados, Escravos and Benin rivers areas on the western fringe of the Delta. The
mangrove oyster is plentiful in the brackish-water creeks in the Delta, generally attached
to the aerial roots of the mangrove trees, at intertidal levels. Table 1 shows a summary
of the potential aquaculture species of finfish and shellfish in Nigeria.

The Nigerian coastal environments are under-exploited in both finfish and shellfish
fisheries. This is because peasant fisheries are still dominant. Both the Federal and
State Governments are gradually finding answers to the maximum exploitation of our coastal
waters.

The following is a very brief description of the fishing gears used along the four
major zones of the Nigerian coast.

3.1 Bag Net

A conical bag of light cane bound with raffia palm fibres, some 8–10 m in length by
approximately 4 m across the menth. It is set on stakes in batteries of 2–4 pieces, and
fishes during the ebb and flow of the spring tides only. The bag net captures prawns,
other crustaceans and finfish.

3.2 Basket Trap

Consists of a conical basket 1.5–2 m in length by 3/4 m across the mouth, woven from
the midrib of the fronds of the 'palm-wine tree' (Raphia vinifera). Across the mouth of the
trap there is a rope of bridle of a local creeper. The trap is set by passing the bridle
over a stake, driven into the bottom of the estuary and then pushing the trap to the bottom
by means of a long pole. The traps are usually set at low water and fish during the flood
tide, but they may also be set to fish the ebb. As might be expected, catches are best
during spring tides when currents are strongest. They fish by day or by night and, in
general, the best catches are from those set in 3–5 fathoms on a mud or sand-and -mud bottom
near the sea. Further upstream, in shallower water, the catches decline.

3.3 Brush-Wood or Leaf Trap

A row of leaf branches or bundles of twig tied to stakes, driven into the bottom of
the creek or river. The shrimp and prawns gather in these and are captured by hand nets,
or they are lifted out of the water and the prawns are beaten out of them.

3.4 Canoe-Screen

A square of netting of 3–4 m sides; three sides are attached to a wooden frame, the
fourth side to the gunwale of a canoe. It has supporting lines from the canoe to the far
side of the frame to raise the net. The net is dipped into the water and small fish and
prawns scooped into the canoe, which is moved along the edge of the river or creek, sieving
the catch out.

3.5 Cast Net

A cone of netting weighted round the base and so constructed that, when held at the
apex and properly thrown, the net spreads out, strikes the water in a circle and sinks
quickly to trap the fish under it. Cast nets are of various sizes: (2–4 fathoms deep and up
to 16 m in diameter when cast) and meshes (50–55 mm for small bonga, 60 mm for large bonga,
25–50 mm for fishing small mullets and tilapias), and may be specially adapted for certain
species of fish. The bottom of the net is usually caught up to form pockets for capturing
fish, particularly mullets and tilapias.

A fisherman may own as many as 20 cast nets and each man may carry 3–5, when fishing,
although only one is used in a canoe at any one time. Cast-netting is a very effective
fishing method in the Delta but is on the whole a young man's technique, as it requires
great physical effort (Scott, 1966).

3.6 Fishing Stake/Enclosure

A single row (or two converging rows) of stakes, driven into the bed of a river, creek
or estuary, and leading into an enclosure in which fish, moving along the line of stakes,
are trapped. The enclosure is formed of wooden screen supported by stakes or, more usually,
of thin stakes bound to each other to form a screen through which water can flow but from
which fish cannot escape. The opening into the enclosure to which the line of stakes leads
is large enough to allow fish to enter, but its edges curve in to make a non-return entrance.
The enclosure may be a single chamber, heart-shaped or triangular, or 2–3 chambers each giving
access to the next, thus making more difficult for fish to escape.

Fishing stakes are usually set on the edge of sand banks or out of the edge of the creek.
The enclosure may have mud piled up in it, so that it dries out at low water, and the fish
are stranded, or the fish may be scooped out by hand nets.

3.7 Gillnet

A rectangular sheet of netting, fixed to a headling on top and usually to a foot rope
at the bottom. The headline is fitted with floats to hold the net upright, the floats being
fixed directly to the headline or on lengths of line so adjusted as to make the net fish at
a given depth below the surface.

The foot-rope is usually weighted by attaching to it pieces of iron, concrete, shells.
Fish are captured when they swim into the net, either being caught by their gills or by their
fins, spines, etc. The gillnet may be operated in a number of different ways:

As a set-net: the foot rope is weighted and is anchored to each, so that
the net fishes at the bottom, in a fixed position, sweeping only a limited
area with the tide.

The small-mesh set nets are used near the edge of creeks mainly for drum, the
shoals of which are sometimes located by the fishermen listening for them
either under the water or by dipping the paddle into the water and listening
to the vibrations which travel along the blade to the handle. These techniques
are used in other parts of the world in fishing for small sciaenids which make
croaking noise both in and out of the water.

The large-mesh set nets are used in the rivers, estuaries and large creeks for
capture of croaker, threadfin, barracuda, catfish and also the larger drums.

As a dragnet: the foot-rope is lightly weighted so that the net drags on the
bottom, but is moved along with the current.

As a drift net: the foot-rope is lightly weighted or unweighted, or may even be
absent. The net drifts freely with the current. Drift nets are used in the
larger creek estuaries and rivers, their catches depending on the mesh of the
netting as in the case of the set nets. They are particularly effective for
shad, bonga and other small shoaling fish.

As an impounding or encircling net: the net is set in a circle round a shoal of
the fish and the fish are then driven into the net by splashing the water within
the net.

Gillnets vary considerably in size and mesh, but are generally 15–30 fathoms long
and 0.5–5 fathoms deep. The mesh varies according to the fish sought. For bonga
and small fish, it is about 50 mm (stretched), ranging up to 100–150 mm in large
set nets and to 230 mm or more in shark nets. The smaller-mesh nets are usually
so deep as those of larger mesh. The net is usually set on almost straight with
little flow or ‘bunt’. The traditional cotton netting is being rapidly replaced
by synthetic netting, although the head-and-foot ropes are usually cotton.

The netting is usually bought by the piece and then set up by the fisherman, but
some fishermen still weave their own nets and most experienced fishermen are
skilled net-makers.

3.8 Hand Net

A circular hoop of about 0.75 diam., to which is attached a 1 m long bag of fine-mesh
net. The operator moves along the shallow water at the edge of a creek or sand bank,
sieving the water for small fish and prawns. It is usually used by women for food for the
family.

3.9 Light Fishing

Lights may be used in conjunction with any of the methods used for surface or shallow-water
fish (drift nets, set nets, stakes, beach seines, canoe screens) to attract fish into
the area where they can be caught.

3.10 Line

A length of strong fishing twine to which is attached, at intervals, a number of hooks
on short side-pieces of finer twine (snoods). The size and number of the lines and hooks
varies from lines with a score of hooks as used by women for subsistence fishing, to several
hundred hooks as in the unbaited-hook fishery for rays.

A variety of baits is used, such as small prawns, for the small lines and pieces of fish/live fish, when fishing for large fish. The most unusual bait which is in common use in
some areas is carbolic soap. It is effective but is said to impart an unpleasant flavour
to the fish.

The lines may be shot across the current, but are usually shot with it and are anchored
by heavy weight at each end to which is attached a calabash or shaped piece of wood as a
marker float.

3.11 Screens

Of raffia palm mid-ribs which are fixed parallel to the edge of the creek to from
ponds or as enclosures in shallow areas. The crustaceans and small fish are trapped by the
screens as the water drains into the creek or ebbs from the shallows. The screens may be
used in conjunction with a non-return trap which is placed in the main drainage channel into
which the catch is funneled.

3.12 Seine

A triangular bag of netting with extensions on each side, to which are attached long
ropes. The ropes and net are set to encircle a shoal of fish and then the ropes are hauled in,
driving the fish into the centre of the encircled area where they are eventually trapped in
the net. Seines may be operated from the shore (beach-seine) or from boats off-shore
(e.g., Danish seine).

3.13 Snag Hooks

Group of unbaited hooks set at intervals along a line, on the creek or river-bottom.
Fish, mainly rays, are pierced by the hooks as they move along the bottom.

3.14 Trammel Net

A set net consisting of a loose, small-mesh net which is mounted between two large-mesh
nets, all three nets being mounted on the same head-and-foot ropes. It is essentially an
entangling net, large fish being enmeshed in pockets of small-mesh netting formed when they
force their way through, but it also acts as a gillnet for smaller fish and thus is effective
against a wide size-range of fish.

3.15 Traps

Various types of basket-traps are used along the Nigerian coast. Apart from traps for
prawns, which is an open cone relying on the force of the current to prevent the prawns from
escaping, some other traps are woven containers with a single incurving, non-return entrance,
either tubular or slit-like. They range from small, purse-shaped mudskipper and crab-traps,
about the size of a briefcase, to cylindrical fish traps about 1.25 m long and 0.5 m in diam.
They may be baited or unbaited, the latter's attraction being the shelter they afford. They
are usually woven from raffia fibre.

3.16 Trawl

A triangular bag of netting with extensions on each side (wings) which is towed by wire
or rope-leads along the seabed behind a boat, to scoop up fish and prawns.

3.17 Trigger Hook

A stick, driven vertically into the mud, to which is attached a line and baited hook,
held under tension by a trigger arrangement. When a fish takes the bait the trigger
mechanism is released and the stick straightens up, usually pulling the hooked fish clear of
the water to avoid the catch to be taken by predators.

Jurisdiction over property (i.e., on land and water) rests with the Federal Department
of Lands in the Federal Ministry of Works and Housing. In the Northern States (i.e., Kano,
Kaduna, Sokoto, Burno, Bauchi and Gongola), land had always belonged to the crown, whereas,
until recently, in the southern states, private ownership (by individuals, family or community)
was the rule. Introduction of the ‘Land Use Edict’ about two years ago has made all property
(undeveloped land and water) in the country essentially crown property. The implication is
that individuals or corporate bodies now have certificate of occupancy for a piece of property
on a leasehold basis, instead of the former freehold conveyance, which enabled individuals/corporate body to transfer the property freely. Under the present arrangement the property
reverts back to the crown at the expiration of the certificate of occupancy, if unrenewed or
revoked by the Government. The Government is able by this arrangement to provide several
people with land for various purposes rather than concentrate it in the hands of a few rich
individuals or families.

Establishing a coastal fish farm involves the procurement of a suitable parcel of land
for the fish farm, and registering the farm as a business venture, depending on its size and
the capital outlay. Under the private ownership of property, it would have been necessary
to check from the Lands Department the correct owner of the property, and having settled
with the correct owner, to re-register the property so that the title deed would reflect the
new owner. However, with the new arrangement of Land Use Edict, what is required is to
identify the suitable parcel of property and to apply to the appropriate authority to allocate
the said property for establishing a fish farm. Unless there is a superior claim on the
property from another Government development interest, it would usually be allocated for a
specified period and a nominal annual rental. Having obtained the property, the next step
would be to register the fish farm, especially if it is on a commercial scale, with the
Ministry of Trade in accordance with established regulations. It is equally useful, although
not a legal prerequisite, to inform the Federal Department of Fisheries of the existence of
such a fish farm in anticipation of the Fisheries Department's function to the entire
fisheries industries.

Extension service to support aquaculture development are provided by the Federal
Department of Fisheries and the various State Department of Fisheries in the country. Fish
seed, feed, fertilizer and equipment for pond construction are provided by the Federal
Department of Fisheries at subsidized rates. Also, technical assistance is provided to crop
or harvest ponds, and cold stores are provided on payment of nominal hire charges. The list
of items and the rates of subsidy are shown below:

At the moment, conflict between aquaculture in the coastal areas and other developments
would appear to be minimal, if indeed it exists. One major reason is that the bulk of usable
property for coastal aquaculture is essentially rural swampland that attracts virtually no
industrial, agricultural, housing or tourist investment for development. However, it must
be emphasized that the recent Government philosophy of integrated rural development coupled
with the natural urban spread could result in coastal aquaculture actively competing with
industries, housing and even tourism because some of these rural swamplands have peculiar
exploitable beauty of theirs. We envisage such a situation to arise when effective, and
cheap building technology and good communication with the rural areas have been developed.
It is perhaps pertinent to state that in a recent developmental conflict between fishing
and trade for a parcel of rural swampland to the west of Lagos, it was trade that won, as
evidenced by the existence of the Tin Can Island Port Complex.

Fish production from all sources is estimated at 495 000 t, while actual demand reaches
869 000 t, based on an average per caput consumption of 11 kg and a population of 79 million.
The actual deficit amounts to 374 000 t. This figure could be higher because of the
increases in incomes and the consequent higher purchasing power. The deficit in fish demand
must be balanced although it is unlikely that it will be entirely from capture fishery,
because there is a limit to the expansion of the demersal fisheries. An alternative method
of fish production that could bridge the gap is aquaculture.

From observations and reports, it appears that a large part of the country's 1.8 million ha
of swampland (fresh and brackish) could be converted into viable fish ponds. Assuming that
only 50 percent (or 900 000 ha) of the swampland could be made to produce annually 1 t/ha,
about 900 000 t of fish could be provided to bridge the gap in fish demand, and also offset
imports of over Naira 1 billion per year.

Location of the swamplands in the rural areas and the possible creation of the forward
and backward linkage industries in other sectors of agriculture, would increase the economic
activity of the rural areas. This would generate employment and thereby help reducing the
actual population drift.

In addition to the subsidized inputs already listed, financial assistance is also
available under the Agricultural Credit Guarantee Scheme Fund. By this scheme, a fund,
amounting to Naira 100 million, was established in 1977. Sixty percent of this amount was
subscribed by the Federal Military Government and 40 percent by the Central Bank of Nigeria.

The fund was to provide guarantee in respect of loans granted by any bank to farmers
for agricultural purposes, including fish farming. The maximum liability of the fund in
respect of any gurantee given under the scheme was to be fixed periodically by the
Commissioner for Finance. At the moment, individuals can get up to a maximum of Naira 50 000
while a cooperative society or a corporate body can get a maximum of Naira 1 million. The
interest rate chargeable by banks on credit facilities provided under the scheme, was to
be as prescribed by the Finance Commissioner. As at now, the interest rate chargeable on
loans to cooperative societies is 4 percent per year, while in other cases the rate is
6 percent per year.

Other financial incentive to promote agriculture, which includes aquaculture development,
are: a 5-year tax holiday for investors in combined agricultural production and processing,
abolition of import duties on machinery and equipment used for agricultural production, and
the removal of import duties on new materials for the manufacture of livestock feeds.

When aquaculture is considered against the background of total fish production and
demand in the country, the potential for aquaculture is enormous. This potential could be
realized only under the correct financial climate and availability of the appropriate
technology. The Federal Government is providing the necessary financial climate, while
institutes involved with aquaculture research and development are working towards providing
the required technology.

One major problem of aquaculture is the demonstration of its economic viability.
Bad planning and management, coupled with lack of the right technology, would appear to have
portrayed aquaculture endeavours, so far as economically unviable. In order to attract
investors, therefore, there is a great and urgent need to demonstrate through better planning
and effective management the economic viability of aquaculture. Notwithstanding the fact
that Nigeria's oil drilling activities are in the creeks and relatively near the coast, very
little crude oil pollution has been reported until now. The situation is being monitored
constantly. One source of pollution that requires careful monitoring, considering the
danger it poses, consists in the effluents discharged from the chemical industries, which
are increasing daily in number and size.

Has given good results in brackish water. Experiments in fresh water under way

Clarias lazera

very good

year round but inadequate

Omnivorous, supplementary feeds

0–25

Can be stocked very densely provided supplementary feed is given. Now cultured with tilapias

Heterotis niloticus

low

seasonal and inadequate

Phyto- and zooplankton

freshwater only

Small sizes favoured. Larger sizes said to be of lower taste

Ethmalosa fimbriata (Bonga)

good

seasonal ?

Phytoplankton

0–35

Comes into ponds with the tide. Appears to be sensitive to oxygen deficiency, delicate and does not keep long once out of water

Penaeus durarum

very good

seasonal

Detritus of both plant and animal origin

0.5–35

Comes into ponds with the tide. Delicate and limbs easily damaged. Has grown to about 20 g in ponds

Macrobrachium spp.

very good

seasonal

Detritus of both animal and plant origin

Fresh to about 10

Caught in abundance in certain areas of the country

Lates niloticus

very good

scarce

Predatory

Fresh water only

Good predator species for tilapias, but preys on carps also. Fast growth

Hemichromis fasciatus

low

adequate

Predatory

0–26

Good predator species for tilapia. Does not grow beyond about 20 cm. When grown with large carps, feeds on tilapia fry and fingerlings only

Lutjanus apodusLutjanus agennes

good

inadequate

Predatory

1 - above 30

Good predator species for tilapias in brackish-water ponds

Gymnarchus niloticus

good

inadequate

Predatory

Fresh water only

Good predator for tilapias. Fast growth

Elops lacerta

low

inadequate

Predatory

1–26

Comes into ponds with the tide. Delicate and sensitive to oxygen deficiency, does not keep long out of water

Crassostrea gasar

good

almost throughout the year

Phytoplankton

2–32

Spat settles better on hard timber than old oyster shells or asbestos. Better settlement in the shade than in open areas. Settlement more abundant in depths between about 30 cm and 100 cm from water surface. Available all along the coastline in the brackish-water areas. Can grow to about 8 g (wet meat) in one year under natural conditions

Heterobranchus bidorsalis

good

seasonal

Omnivorous

Fresh water

Responds well to fertilizer and supplementary feeding

Distichodus engycephalus

good

seasonal

Herbivorous

Fresh water

Some ponds are noted for excess grass and weeds. These species are suspected to keep weeds under control

Distichodus brevipinis

good

seasonal

Herbivorous

Fresh water

-

Distichodus rostratus

good

seasonal

Herbivorous

Fresh water

-

Malapterurus electricus

good

seasonal

Predator

Fresh water

Good predator species for excess tilapia in ponds

Megalops atlanticusPomadasys jubelini

good

seasonal

Predator

5–30

Comes into pond with tide. Good predator species for excess tilapia in brackish-water ponds

A monoculture study of the catfish, Chrysichthys nigrodigitatus (Lacépède) was undertaken
between January 1976 and July 1977, in brackishwater ponds off the shores of Lagos
lagoon, using groundnut cake as the main supplementary feed. Data obtained included food
conversion values, condition factors, length-weight relationships, survival and growth.
Remarkable differences existed in lengths and weights of fed and unfed catfish. For the
unfed catfish, there was a gain in weight of 114.1 percent compared to 858.1 percent for
fed catfish.

The Nigerian coast is characterized by extensive stretches of swamps and shallow areas
not utilized for any other profitable form of agriculture. If the catfish (Chrysichthys
nigrodigitatus) could be grown in brackish waters unsuitable for any other crop, then a
promising catfish industry awaits the coastal waters of Nigeria. In a continuous search
for cultivable indigenous species, the catfish (Chrysichthys nigrodigitatus) was chosen in
this project for initial monoculture studies. The research ponds are located very close to
the shores of the Lagos Lagoon (Fig. 1). This paper reports on survival under varying
salinity fluctuations, food conversion values, condition factors, length-weight relationship,
and economics of production.

Three 0.41 ha excavated ponds and one 0.25 ha enclosure (open pond), built with 6.25 mm
nylon mesh very close to the lagoon, were used in this project. The excavated ponds and
open ponds were 0.75 m deep at the shallow edges and 1.5 m in the middle. The water supply
came from the Lagos Lagoon and was fed to the ponds during high and low tides through a
regular channel (Fig. 1). The water entering the ponds through a gravel-filled gate for
filtration, was clear and fluctuation of the water level depended on the tide.

At the start of each experiment, the three excavated ponds were emptied and left dry
for one week before liming. The effects of liming on a pond are quite considerable,
especially when the bottom is too muddy and the organic content is too high, which may lead
to oxygen depletion. Soil pH before liming was determined. The dried ponds were limed at
the rate of 550 kg of calcium oxide (quicklime) per ha. In the open pond, the lime was
spread on the water from a boat.

In many warm-water fish ponds, the essential aim of fertilization is the development of
plankton. Since the catfish is a bottom feeder and in its natural environment feeds on
organisms that have plankton as their primary source of food, phosphate fertilizer was
applied only once in the four ponds at the beginning of each experiment. The fertilizer was
applied a week after liming, at the rate of 30 kg triple superphosphate per ha.

The ponds were then filled with water. The fish stocked were of the same size and
averaged 15.6 cm in total length. Feeding began on the second day after stocking and
continued for a period of nine months (271 days). There was no feed for the control pond.
The feed consisted of groundnut cakes, a waste by-product obtained after extraction of
oil by commercial firms in Northern parts of Nigeria. It was given twice daily, at the
rate of 0.65 kg in the morning and 0.65 kg in the evening. Each distribution represented
approximately 10 percent body weight of the fish stocked.

After nine months of stocking, the ponds were drained, the fish were harvested, sorted
into groups, counted and weighed. The standard and total lengths measurements were also
recorded of each specimen.

The length-weight relationships were based on the average measurement expressed
logarithmically, as log W = log a + b log L, where W is the live weight in grammes and L is
the total length in millimeters.

The catfish were harvested after nine months of stocking. Details of the lengths and
weights of the harvested fish from both the fed and unfed ponds are shown in Table 1 and
illustrated in Figures 2 and 3. Figures 4 and 5 show the scatter diagram of the length-weight
relationship of the harvested catfish.

Pond I recorded the highest yield with a total net gain in weight of 7.12 kg, followed
by Pond III (73.11 kg) and Pond II (56.02 kg). In the second growth period, Pond I again
recorded the highest yield with a net gain of 38.20 kg, while Pond II had 29.83 kg and
Pond III 26.73 kg. The control pond had poor yields, with 9.54 kg and 3.9 kg net weight
gains, respectively. There was thus an appreciable difference at harvest between the fed and
unfed fish. Average gain in lengths during the first experiments were 20.4 cm (Pond I),
17.7 cm (Pond II), 20.3 cm (Pond III) and 9.4 cm (Pond IV). In the second experiments,
average gains in lengths were 16.0 cm (Pond I), 14.2 cm (Pond II), 13.6 cm (Pond III) and
6.2 cm (Pond IV). Growth was remarkably slow during the first experiments with a mean of
5.9 g for the three ponds. In the second experiments the growth values were 9.22 g (Pond I);
11.81 g (Pond II) and 13.18 g (Pond III) with a mean of 11.40 g for the three ponds. On
the basis of the above values, it could be concluded that Pond I, during the first period,
had the best food conversion value (FC = 4.45), while Pond III of the second growth period
had the worst one (Tables 6 and 7). The mean food coefficients for the three ponds were,
respectively, 5.19 and 11.40 during the first and the second growing periods. To what
extent pond food organisms contributed to these differing values could not be ascertained
in this project.

Length-weight relationship of C. nigrodigitatus for the two treatments - fed and unfed
fish - are shown in Figures 4 and 5. When the data were compared, the functional regression
value ‘b’ for the unfed fish was 3.0171, while the value ‘b’ for fed fish was 4.8642. The
two treatments exhibited an allometric growth (Ricker, 1975) because of the changing body
forms, stomach contents and development of the gonads. Since the length-weight regression
value is a relative measure of condition, the above difference between the ‘b’ values could
be interpreted as a measure of difference in condition between the groups which changed in
size throughout the growth experiment.

The regression equation Log weight = Log a + b Log length was calculated for the two
treatments. For the unfed ponds the equation was:

Log weight = - 2.3344 + 3.0171 log length

and for the fed ponds it was:

Log weight = - 4.9687 + 4.8642 log length

In its natural environment, some workers calculated the above values for C. nigrodigitatus.
Ajayi (1972), in his general studies of the Bagridae in Kainji Lake, calculated the
corresponding regression equation to be:

Log weight = - 1.90 + 3.012 log length

Ikusemiju (1973), in his length-weight calculations of C. nigrodigitatus in the Lekki
lagoon, had the regression equation:

Log weight = 12.0851 + 3.0177 log length

On the basis of the above values, remarkable difference in growth existed between fed
and unfed specimens of C. nigrodigitatus.

The groundnut cakes feed used in this project is available as a waste surplus at many
oil mills in the northern part of Nigeria. Compared with other local feeds like the palm-kernel
cake and bran sweepings from rice mills, it has a much higher protein content
(Kent-Jones and Amos, 1957). Because this feed was not manufactured commercially according
to international standard and requirements of protein, carbohydrate, vitamins and minerals,
the standard feeding rate of 3 percent body weight was not followed. Rather 10 percent
was applied in the morning (10.00 h) and 10 percent in the evening (16.00 h). This feeding
ratio (approximately 1.3 kg daily) was observed throughout the growth periods to avoid water
contamination or oxygen depletion, to ensure that not much feed was lost to the mud and
hence to the fish, and also to avoid fish contamination by aflatoxin, the toxin produced by
Aspergillus flavus and present in corn, peanuts and cotton-seed (Lovell, 1977).

Similar approaches to experiments on local feeds in Nigeria have been adopted.
Maclaren (1949) reported that crushed hermit crabs at the rate of 0.5 kg per 0.1343 m2
produced the optimum yield in small ponds, stocked with C. nigrodigitatus. Increased rates,
he observed, produced no appreciable effect, even when combined with heavy stockings of
small fish. Zwilling (1963) fed fish species with spoiled groundnuts, guinea corn and
groundnut cakes at a chosen rate of 4 percent of the initial weight. Sivalingam (1972) tried
common carp (Cyprinus carpio) with groundnut cake at an arbitrarily chosen rate of 2.5 kg,
plus a 135-g cup of palm oil.

In countries advanced in fish farming, the 3 percent body weight feeding rate is
gradually being revised to take account of other factors. Perry and Avault (1971) in their
polyculture trials of blue, white and channel catfish in brackishwater ponds, applied to the
ponds 0.09 kg mixture of one-fourth floating and three-fourths sinking feed rations until they
were accustomed to the floating type. The feeding rate was later dropped to the standard
3 percent body weight of a commercially compounded floating feed. Cowey et al., (1972), in
their studies on growth rate and conversion ratio of the flatfish, arbitrarily selected
daily feeding ratios: fish of 12–13 g were fed a pelleted diet twice daily, 6 days a week
at rates varying between 0.5 g dry ration/100 g biomass and 2.5 g dry ration/100 g biomass.
Bergstrom (1973) investigated the effect of different levels of dietary fat, protein and
carbohydrates on growth and survival of Atlantic salmon. No harmful effects were noticed
at the various rates as high a percentage as 20 percent of the diet. In 1975, Professor Marck
of the Ministry of Agriculture in Israel (cited by Tom Lovell, 1977a), proposed a revision
of the feeding table for carp in ponds in that country in order to take into account the
nutrient contribution of natural food. He demonstrated that the carp obtained 4.8 kg of
protein per ha/day from natural pond food. Lovell (1977a) observed that in intensely fed
ponds, channel catfish received only 14.18 kg of digestible protein and 83.3 calories of
digestible energy from pond food organisms during a 180-day period.

In view of experience of previous workers in both advanced and developing countries,
more research work is worth carrying out on local feeds in Nigeria to determine feeding
rates and also improve their protein, carbohydrate, fat, vitamin and minerals contents for
maximum fish production in ponds.

The future prospects for the catfish industry in Nigeria are very bright. If fully
developed, it could contribute largely toward meeting the demand for fish. The species
grows well in both fresh and brackish water. This section considers the estimated costs,
running costs and returns for monoculture trials in a brackish-water fish farm. Details are
shown in Appendix 1. Costs, naturally, would depend on the layout of the land, the amount
of clearance to be done and the cost of water supply.

4.2.1 Water supply

Adequate water supply is a prime factor. On relatively level land, water must be
supplied by streams, springs or wells. Streams generally provide a low-cost water resource
for the fish farmer, though diseases and wild fish stock could easily be introduced into
the ponds. A prospective fish farmer must balance the risks associated with smaller water
delivery systems against the costs of larger systems.

4.2.2 Land charges

Price of land varies depending upon several factors. In brackish-water areas, the land
is swampy and could not possibly be put to other profitable agricultural enterprises.
Purchase of land from such swampy areas in Nigeria is relatively very cheap. Location of
land can however modify its value. In the inland areas, land is more costly since such
lands could easily be converted to other uses. Before committing resources to pond
construction, the farmer should carefully weigh alternative uses of his land and financial
resources available for his fish farm project.

4.2.3 Pond construction

The costs depend on nature of land and ground water. Earlier research has indicated
that cost per surface hectare of water decreases with increased pond sizes. Some authors
have recommended the building of rectangular ponds of about 8 ha. Coverage of the ponds
with feed, they observed, is enhanced and harvesting problems and costs are reduced when
8-ha ponds are used. In southern United States of America, an 8-ha pond stocked with
6 250 catfishes/ha would contain approximately 22 727 kg of fish at harvest. Larger ponds
would extend the harvest period and increase the risk of death loss among live hauled fish.

4.2.4 Other accessories

Other items required include nets and fishing equipment for harvest and sampling
exercises, storehouse for lime, fertilizers and feeds, canoes, fertilizers, feeds, chemicals,
simple water quality kit and general store used as service building.

4.2.5 Labour

The manpower requirement will include fishermen, and the fish farmers for pond
maintenance, feeding, water-quality monitoring and other duties. Labour requirements are
estimated in the pilot project and are included in the operating costs.

4.2.6 Operating costs

These include such items as purchase of fingerlings, feeds, lime and fertilizers.
Operating costs are sometimes called variable costs, since they change depending upon the
level of production. Fingerlings and feed costs make up over 60 percent of operating costs
and it is very important that high quality is obtained when purchasing both items. Net
returns represent the difference between total costs and total returns. The net returns
generally are a payment to land, unpaid family labour, capital and management used in
production. Principal payments on land and capital items must be withdrawn from net
returns to determine returns to management and unpaid family labour.